This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2006-163602 filed in Japan on Jun. 13, 2006, the entire contents of which are hereby incorporated herein.
The present invention relates to an optical wireless communication device mounted in electronic equipment.
As widely known, IrDA 1.0 and IrDA 1.1, standards for optical wireless communication devices that allow wireless communication between different pieces of equipment using light, were established in 1994. These standards do not require the formation of networks and readily allow peer-to-peer (one to one) communication. Currently, they are implemented mainly in cell phones, and are expected to be implemented in printers and television receivers in the future.
Optical wireless communication devices as described above, which are mounted in, for example, cell phones, function mainly to communicate small-volume text data such as telephone numbers and e-mail addresses. If they are mounted in printers and television receivers in the future, the need will arise to communicate still images and moving images. Along with this need, higher speed communication as well as an extension of communication distance will be required.
The IrDA 1.2 standard for optical wireless communication devices provides lower power consumption for infrared communication devices.
Although there exists a strong demand for higher communication speed and extended communication distance, satisfying these two requirements requires more power consumption.
In other words, increasing communication speed and communication distance is contradictory to providing lower power consumption, and therefore it is difficult to satisfy these contradictory requirements.
In view of this, JP 2005-328360A proposes to execute a shutdown mode during which almost no current flows while no signal is present, so as to reduce the power consumption of a device. More specifically, as shown in the flowchart of FIG. 3, when the shutdown mode is executed during the stand-by state (step S101), the control unit determines whether or not to permit communication (step S102), if it determines not to permit communication (i.e., when “No” is selected in step S101), the shutdown mode is maintained. If the control unit determines to permit communication (i.e., when “Yes” is selected in step 102), communication is carried out (step 103). After the completion of the communication, it switches back to the shutdown mode. This reduces the power consumption while the device is does not communicate.
Also, according to JP 11-112431A, a light-emitting element is allowed to emit radiation at a minimum intensity that does not affect communication quality so as to reduce the power consumption of a device.
However, even if shutdown mode is executed while no signal is present as disclosed in JP 2005-328360A or a light-emitting element is allowed to emit radiation at a minimum intensity as disclosed in JP 11-112431A, the power consumption of a device will be reduced only slightly, and these techniques cannot achieve both an increase in communication speed and communication distance and a reduction of power consumption to a lower level as described above.
The present invention has been accomplished in view of the problems encountered with such conventional techniques. It is an object of the present invention to provide an optical wireless communication device capable of both increasing communication speed and communication distance as well as reducing power consumption to a lower level.